Steven J. Anderson

Epstein-Barr Virus LMP2A Drives B Cell Development and Survival in the Absence of Normal B Cell Receptor Signals

Epstein-Barr virus (EBV) establishes a persistent latent infection in peripheral B lymphocytes in humans and is associated with a variety of malignancies and proliferative disorders. Latent membrane protein 2A (LMP2A) is one of only two viral proteins expressed in latently infected B lymphocytes in vivo. LMP2A blocks B cell receptor (BCR) signal transduction in vitro by binding the Syk and Lyn protein tyrosine kinases. To analyze the significance of LMP2A expression in vivo, transgenic mice with B cell lineage expression of LMP2A were generated. LMP2A expression results in the bypass of normal B lymphocyte developmental checkpoints allowing immunoglobulin-negative cells to colonize peripheral lymphoid organs, indicating that LMP2A possesses a constitutive signaling activity in nontransformed cells.

A dominant-negative transgene defines a role for p56lck in thymopoiesis.

The lymphocyte‐specific protein tyrosine kinase p56lck participates in T cell signaling through functional interactions with components of the T cell antigen receptor complex and the interleukin‐2 receptor. Additional insight into the function of p56lck has now been obtained through the generation of transgenic animals expressing high levels of a catalytically inactive form of this kinase (p56lckR273). Mice bearing the lckR273 transgene manifested a severe defect in the production of virtually all T lymphocytes. Those exceptional CD3+ cells that escaped the effects of the lckR273 transgene were confined primarily to the T cell subset that expresses gamma/delta T cell receptors. Remarkably, construction of a dose‐response curve for the effects of the lckR273 transgene revealed that developmental arrest of thymocytes occurred at a discrete stage in the normal T cell maturation pathway, corresponding to a point at which thymoblasts ordinarily begin a series of mitotic divisions that result in expansion and maturation. These results suggest that p56lck normally regulates T cell production by metering the replicative potential of immature thymoblasts.

Inhibition of T-cell receptor beta-chain gene rearrangement by overexpression of the non-receptor protein tyrosine kinase p56lck.

The variable region genes of the T cell receptor (TCR) alpha and beta chains are assembled by somatic recombination of separate germline elements. During thymocyte development, gene rearrangements display both an ordered progression, with beta chain formation preceding alpha chain, and allelic exclusion, with each cell containing a single functional beta chain rearrangement. Although considerable evidence supports the view that the individual loci are regulated independently, signaling molecules that may participate in controlling TCR gene recombination remain unidentified. Here we report that the lymphocyte‐specific protein tyrosine kinase p56lck, when overexpressed in developing thymocytes, provokes a reduction in V beta‐‐D beta rearrangement while permitting normal juxtaposition of other TCR gene segments. Our data support a model in which p56lck activity impinges upon a signaling process that ordinarily permits allelic exclusion at the beta‐chain locus.

An activated Ick transgene promotes thymocyte development in rag-1 mutant mice

Expression of the T cell receptor beta (TCR beta) chain is necessary for the transition from the CD4CD8- stage in the major alpha beta thymocyte lineage. The protein tyrosine kinase p56lck has been implicated in the regulation of early thymocyte differentiation and of allelic exclusion at the TCR beta locus. Using mice overexpressing an activated lck transgene and mice with a disruption of the lck gene, we demonstrate that p56lck participates in a pathway that regulates the expansion of the pool of CD4+CD8+ thymocytes to wild-type levels. In addition, p56lck may be involved in the down-regulation of the putative pre-TCR on CD4+CD8+ thymocytes.

Involvement of the Protein Tyrosine Kinase p56lck in T Cell Signaling and Thymocyte Development

Publisher Summary This chapter discusses current information relating to the structure and the function of p56 lck and focuses special attention on the increasingly well-defined role of p56 lck in controlling thymocyte development. The first of the kinases to be described and the most thoroughly examined is the lymphocyte-specific protein tyrosine kinase p56 lck . The lessons deduced from investigating p56 lck behavior have had a broad impact on the study of nonreceptor protein tyrosine kinases in general, especially those of the src family. The 509 amino acid lck -encoded protein represents a typical, membrane-associated nonreceptor protein tyrosine kinase of the type exemplified by p60 c-src . Nine distinct members of the src family have been identified, and all share common structural features. Following gentle cell disruption, p56 lck behaves as if part of a large, detergent-insoluble membrane and cytoskeletal complex that includes a number of cell-surface receptors, for example, the glycosylphosphatidylinositol-linked molecules Thy-1 and Ly-6. Some evidence suggests that these proteins, acting via some transmembrane intermediary, may also be capable of stimulating p56 lck activity. Thymocyte differentiation proceeds in an ordered and stepwise fashion in generating mature T cells from bone marrow-derived precursors. This pathway is divided into two phases, each requiring distinct molecular events for continued development. Several lines of evidence, primarily from analysis of in vitro cell line models, are presented to demonstrate the role of p56 1ck in mediating signal transduction events during T cell receptor-dependent activation of mature T cells.

Bcl-2 Counters Apoptosis by Bax Heterodimerization-dependent and -independent Mechanisms in the T-cell Lineage

The effect of the cell death inhibitor Bcl-2 in relation to its capacity to dimerize with apoptosis promoter Bax or its homologs at their physiological expression levels was explored in the T-cell lineage. Transgenic mice expressing a BH1 mutant Bcl-2 (Bcl-2 mI-3), which fails to heterodimerize with proapoptotic members of the Bcl-2 family, such as Bax, were generated. Bcl-2 mI-3 protected immature CD4+8+ thymocytes from spontaneous, glucocorticoid and anti-CD3-induced apoptosis and altered T cell maturation, resulting in increased percentages of CD3hi and CD4−8+ thymocytes. In contrast, apoptosis of peripheral T-cells was unaffected by transgene expression. This correlated with their high Bax expression level and insensitivity to the caspase inhibitor, zVAD-fmk, a functional hallmark of Bax-like activity. Thus, within the T-cell lineage Bcl-2 can inhibit apoptosis independent of its association with Bax or its homologs; yet, above a threshold level of their physiologic proapoptotic activity, the capacity of Bcl-2 to heterodimerize with Bax or its homologs appears essential for it to counter cell death.

Studies on the antibody-dependent cell-mediated cytotoxicity (adcc) of thioglycollate-stimulated and bcg-activated peritoneal macrophages.

Abstract Peritoneal macrophages (mφ), activated by Bacillus Callmette-Guerin (BCG) or elicited by thioglycollate broth in vivo in C57BL/6J mice, were compared with regard to their ability to mediate antibody-dependent cellular cytotoxicity (ADCC). The BCG-activated mφ had several times higher ADCC activity than did the TG-mφ against erythroid targets. When human and murine tumor cells were employed as targets in the ADCC assay, the BCG-mφ lysed each of six separate target lines considerably, while the TG-mφ had little and, occasionally no, lytic activity against the six targets. Although F c -dependent and -independent phagocytosis of the erythroid targets by the TG-mφ exceeded that by the BCG-mφ, this rapid and extensive phagocytosis did not account soley for the decreased lysis of the erythroid targets by the TG-mφ. The results indicate that BCG-activated peritoneal mφ, in comparision with TG-elicited inflammatory mφ, are potent effectors of ADCC against both erythroid and neoplastic target cells.

Lower extremity injuries in youth sports

The lower extremity is the most commonly injured anatomic area in sports. An appropriate history and physical examination is sufficient to diagnose most injuries. By knowing the position where a joint has the greatest and least bony stability, one can predict the likelihood of bony and ligament injury. Such information is helpful in determining which structures are most susceptible to injury as well as identifying when radiographs or other diagnostic studies are indicated. An accurate diagnosis is crucial for planning effective therapy and in determining the need for surgical referral. An understanding of common injury patterns is also helpful in differentiating sources of musculoskeletal pain that are not injury related.

Acute Ankle Sprains: Keys to Diagnosis and Return to Play

IN BRIEF: The diagnosis and treatment of acute ankle injuries present challenges to both primary care physicians and orthopedic specialists. Determining the position of the ankle when the injury occurred may help distinguish sprains from fractures so that unnecessary x-rays can be avoided. Stepwise rehabilitation restores function and diminishes the risk of reinjury. Physicians can stress functional measures of recovery to objectively assess readiness for return to play and balance the risks of incomplete rehabilitation against the desire for an early return to sports.

When to Return to Play After an Ankle Sprain

An ankle sprain may not seem like a big deal, but returning to play without proper rehabilitation will increase your chances of injuring your ankle again-maybe even more seriously. Taking the time to fully recover will actually put you back in the game faster. The checklist on the other side of this page will take the guesswork out of knowing when you are ready to return to play safely.